1. Field of the Invention
The present invention relates to a lens unit configured to be capable of being coupled with a camera body so as to be removable.
2. Description of the Related Art
In cameras and lens units which allow an interchange of lenses such as single-lens reflex cameras, the following lens units are in practical use as lens units mountable and demountable with respect to camera bodies. That is, lens units having a mechanism for fixing the lens unit and the camera by fitting claws provided at three or four positions on the lens unit side into corresponding portions on the camera side and turning a lens barrel, thereby allowing a lock pin to be intruded at a certain position to fix the lens unit and the camera body are in practical use. (see Japanese Patent Laid-Open No. 3-231726). Also, in low profile zoom lens units that take into account the portability and the storage property of the lens units, the proportion of the length of a zoom ring to the whole length of the lens unit is high. Therefore, user's hand may be put on the zoom ring when mounting and demounting the lens unit with respect to the camera body in many cases. In this case, since the operation to mount and demount the lens unit with respect to the camera body is performed in a state of holding only the zoom ring, there is a case where only the zoom ring is rotated even though an attempt is made to rotate the entire lens unit, so that a problem of a mounting-and-demounting operability may arise. In retractable lens units having a lens barrel which becomes shorter in entire length thereof in a retracted state than in a shooting state, there is less area which may be held by the hand for rotating the entire lens unit when mounting and demounting the lens, so that a problem of a mounting-and-demounting operability may arise.
In order to avoid this problem, a following retractable zoom lens unit as shown below is disclosed in Japanese Patent Laid-Open No. 10-20176. In other words, Japanese Patent Laid-Open No. 10-20176 discloses a configuration in which a rotary resistance of the zoom ring is increased only at the time of mounting and demounting the lens unit with respect to the camera body in the retracted state is increased and the entire lens unit is allowed to rotate without allowing the zoom ring to rotate at the time of mounting and demounting, whereby the operability is improved. Although the zoom ring is exemplified in Japanese Patent Laid-Open No. 10-20176, it is easily understood that this technology may be applied to a focus lens for focusing or rings for other operations.
In the technology of the related art disclosed in Japanese Patent Laid-Open No. 10-20176 described above, a method of increasing a frictional resistance between a fixed cylinder and the zoom ring is employed as a method of increasing the rotary resistance of the zoom ring at the time of mounting and demounting. However, there is a fear that generation of a high frictional force stably causes an anxiety in terms of durability. In addition, there is a high probability that a rotational operating force applied at the time of mounting and demounting of the lens unit with respect to the camera body is instantaneously increased at the time of operation and an operation ring rotates unexpectedly. In addition, the technology which improves the mounting-and-demounting operability of the lens unit with respect to the camera body only when the retracted state may not be applied to the lens unit which is not retractable.